A hydraulic lash adjuster (HLA) typically comprises a chamber that should be filled with fluid so that the fluid can be compressed and thereby offset cam-related parameters in an engine valve train. The amount of fluid in the chamber can vary based on the moment of use of the HLA in the valve train cycle. That is, the fluid chamber can cyclically be in a compressed (high pressure) and uncompressed (ambient pressure) state and the fluid volume within the HLA may vary dependent upon the point in the cycle. Some HLAs are designed to pull oil in to a first chamber and allow leakdown of fluid out of the first chamber and in to a second chamber as the HLA cycles in the valve train. Some HLAs are designed so that, in use, the pressure differential between the first chamber and the second chamber selectively allows fluid communication between the chambers via a selective transfer mechanism. HLAs may additionally be designed to draw fluid from an external reservoir into the HLA to replenish the fluid within.
Oil is the preferred fluid for the first and second chambers during engine operation. However it is difficult to completely fill the chambers with oil prior to installing the HLA in a valve train. This difficulty is caused by several factors such as fluid viscosity, adhesion, manufacturing actions which result in “pump down” of the fluid, or other fluid motions due to the accommodations for leakdown or accommodations for communication with the reservoir. The difficulties can lead to air in one or both chambers instead of oil. Such an air-containing HLA can be referred to as “spongy” or “pumped down,” and such an HLA may be rejected by end users.
It is important to adequately fill the HLA with the desired fluid prior to installing it in a valve train. This is because the HLA serves a protective function and accommodates variations in cam action or cam tolerances. Air in the chambers results in improper pressurization. The improper pressurization can mean that the HLA cannot satisfy its protective function, and serious engine damage may occur. This damage is especially true for an engine being operated for the first time, or for an engine in a calibration cycle.